It might be easier if you ease into the fast - and have a gentler transition from SAD to fasting. Maybe cut out sugar, caffeine, and processed few for a week, then have only raw foods for a week, then try the juice fast. You might be in for some extreme detox in the next few days. But I appreciate your desire to go into it full speed ahead. I think if I had come upon this juice fast info while SAD I would have wanted to do it, too.
Some tips, if you like to eat a particular fruit or veggie, then you will probably like it juiced. I think one of the easiest juices to drink is carrot apple. It's mild and refreshing. I like almost any combo of fruit juice, because I love fruit. Veggies are a little trickier. Just experiment and have fun. Enjoy it. Update here often, it helps.